Reddit founders just want to cash in. u/spez made $200M last year in compensation which made him one of the highest paid CEO in the bay area. they simply couldn't give 2 fucks about what happens after the IPO, they know their site is a liability , riddled with depravity... and Google wants to train its AI on that crap?
Think about it... Google could train its AI to recognize malicious behavior for moderation purposes, to recognize astroturfing and manipulation of public opinion (for purposes of stopping it or carrying it out).
There's not much value in training it to simulate a redditor, but there's a lot in modeling bad behavior.